Removal of ozone from the atmosphere by soil and vegetation

OZONE is the principal constituent of the photochemical smog that plagues many cities in the United States. Produced by the action of sunlight on the hydrocarbons and oxides of nitrogen emitted by vehicles and industry, concentrations of ozone greater than 25×10¹¹ molecules cm ^-3 (1×10¹¹ molecules cm^-3 =0.4 parts per hundred million = 8 μg m^-3), used as evidence of photochemical smog¹, have been observed in Los Angeles for more than two decades². Because of lower air temperatures, less sunshine and fewer vehicles, photochemical pollution was considered unlikely to occur in Western Europe but concentrations indicative of photochemical smog have now been reported from Germany³, the Netherlands^4,5 and southern England^6,7 on calm, sunny days. High concentrations of ozone cause respiratory difficulties in humans⁸ and damage many plants ⁹ including crops¹⁰.